14998544-Chapter-46-Animal-Reproduction

14998544-Chapter-46-Animal-Reproduction - Chapter 46 -...

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Chapter 46 - Animal Reproduction Chapter 46 Animal Reproduction Lecture Outline Overview: Doubling Up for Sexual Reproduction Concept 46.1 Both asexual and sexual reproduction occur in the animal kingdom Asexual reproduction involves the formation of individuals whose genes come from a single parent. There is no fusion of sperm and egg. Sexual reproduction is the formation of offspring by the fusion of haploid gametes to form a diploid zygote. The female gamete, the unfertilized egg, or ovum, is usually large and nonmotile. The male gamete is the sperm, which is usually small and motile. Sexual reproduction increases genetic variation among offspring by generating unique combinations of genes inherited from two parents. Diverse mechanisms of asexual reproduction enable animals to produce identical offspring rapidly. Many invertebrates can reproduce asexually by fission, in which a parent separates into two or more approximately equal-sized individuals. Budding is also common among invertebrates. This is a form of asexual reproduction in which new individuals split off from existing ones. In fragmentation, the body breaks into several pieces, some or all of which develop into complete adults. Reproducing in this way requires regeneration of lost body parts. Many animals can also replace new appendages by regeneration. Asexual reproduction has a number of advantages. It allows isolated animals to reproduce without needing to find a mate. It can create numerous offspring in a short period of time. In stable environments, it allows for the perpetuation of successful genotypes. Reproductive cycles and patterns vary extensively among mammals. Most animals exhibit cycles in reproductive activity, usually related to changing seasons. This allows animals to conserve resources and reproduce when more energy is available and when environmental conditions favor the survival of offspring. Reproductive cycles are controlled by a combination of environmental and hormonal cues. Environmental cues may include seasonal temperature, rainfall, day length, and lunar cycles. Animals may reproduce exclusively asexually or sexually or they may alternate between the two modes, depending on environmental conditions. Daphnia reproduce by parthenogenesis under favorable conditions and sexually during times of environmental stress. Parthenogenesis is the process by which an unfertilized egg develops without being fertilized. Parthenogenesis plays a role in the social organization of some bees, wasps, and ants. Male honeybees (drones) are haploid, and female honeybees (queens and workers) are diploid. Several genera of fishes, amphibians, and lizards reproduce by a form of parthenogenesis that produces
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14998544-Chapter-46-Animal-Reproduction - Chapter 46 -...

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